The RDB$CONSTRAINTS system table contains the name and definition
    of each constraint. The following table provides information on
    the columns of the RDB$CONSTRAINTS system table.

                                Data
    Column Name                 Type      Summary Description

    RDB$CONSTRAINT_NAME         char(31)  The system-wide unique name
                                          of the constraint.
    RDB$CONSTRAINT_BLR          list      The BLR that defines the
                                of byte   constraint.
                                varying
    RDB$CONSTRAINT_SOURCE       list      The user's source for the
                                of byte   constraint.
                                varying
    RDB$DESCRIPTION             list      A user-supplied description
                                of byte   of this constraint.
                                varying
    RDB$EVALUATION_TIME         integer   A value that represents
                                          when a constraint is
                                          evaluated, as follows:

                                          o  0

                                             At commit time (deferred
                                             initially deferred).

                                          o  1

                                             At verb time (deferrable
                                             initially immediate).

                                          o  2

                                             At verb time (not
                                             deferrable).

    RDB$EXTENSION_PARAMETERS    list      Reserved for future use.
                                of byte
                                varying
    RDB$SECURITY_CLASS          char(20)  Reserved for future use.
    RDB$CREATED                 date vms  Set when the constraint is
                                          created.
    RDB$LAST_ALTERED            date vms  Reserved for future use.
    RDB$CONSTRAINT_CREATOR      char(31)  Creator of this constraint.
    RDB$FLAGS                   integer   Flags.